Apparatus for measuring tensile or compression loads



w. H. ROBERTS 2,403,194

APPARATUS FOR MEASURING TENSILE 0R COMPRESSION LOADAS Filed Nov.' 29V, 194s July 2, 1946.

, Patented July 2, 19,46

* UNITED COMPRESSION LOADS 'y British company Application November 29, 1943,)s'er1a1N0. 512,240 In Great Britain September 30, 1942 v 5 Claims.

. y i 1 AThis vinvention relatesto apparatus for measuring tensile or compressionloads such as in a structural member, or the draw-bar pull of a locomotive, or in general any member of a mechanical" structure which is subjected lto a variable load. A particular application of this invention is' to the apparatus described in United States Patent No. 2,362,308, granted November 7, 1944, wherein it is required to'measure the torque reaction of a prime mover.

According to this invention, a hydraulic double-actingram comprising a relatively reciprocable 'piston and cylinder vis used to convert the tensile or compression load into hydraulic pressure which is measured by a suitable gauge, and

means are provided for adjusting the relative positions of the piston v`and cylinder' at the moment when the pressure, Vand hence the load, is being measured. The making of this adjustment fis desirable in order thatrit can be ensured that the piston is not sticking inthe cylinder, and' that the pressuredeveloped'by the load should always be measured when there is no deiiection or displacement of the rim.

The said means may comprise a pump arranged to deliver liquid into that end'of the cylinder towards whichthe piston has been moved by the applied load, so as to return it to its normal mid'position or any otherv selected datum position." Preferablv, a single pumpisv used, with a change-over valve so that it can supply-either end of the cylindenand the pressure-gauge which is used to measure the pressure corresponding to the load is connected to the "pipe between the pump and the change-overvalve.

It is preferable' also to provide means for opening to drain the end of the cylinder which is not subjected to pressure by the applied load, in order that the pressure on that side of the piston should be constant in al1 circumstances;v if any leakage takes place past' thepiston, as may occur when very high pressures are developed,A such leakage escapes freely to drain and does not introduce any error in the pressure read on the gauge. The change-over-valve'above referred to may be a (Cl. 'Z3-93) 2 e illustrates in section one construction of hydraulic ram, with a diagrammatic layout of the associated parts of the device.

The hydraulic ram comprises a cylinder I closed byend-plates 2, 3, with a, piston vl4 reciprocable invit. The end-plate 3 of thepiston is provided with an axial extension 5 which is formed in any convenientrmanner so as to be capable of being connected to one of the members transmitting the load to be measured.' The piston rod 6 extends at l through the other endplate 2 of the cylinder and is adapted to be connected to the other member bearing Ythe load which isto be measured. The piston rod 6 is also extended intothe end cover 3 at 8 for the purpose hereinafter described.. The piston fl is intended to iioat between, the end-plates of the.

respectively into Vcommunication alternatively,`

with pipes I4 and I5. The pipe |47- is a drain pipe communicating ,with a reservoir I6, whilst the pipe I5 is connected to a pump I1 which draws its supply vfrom the reservoir I6., yThis pump I1 may be o1?v any-convenientiorm and` since it is required to deal only with small quantities .ofV liquid, which however may. have vto -be delivered at a vhigh pressure, it is convenientli'v a lhand-operated reciprocating pump.`

A pressure gauge I8 is connected to the pipe-V show the movements of they-piston in the cylinder duplex one in that it effects the change-over of The single ligure of accompanying drawing and in particular toshow when it is in its Ycentral or datum position in which't is Idesirable that the pressure measurements should be made. The end 8 of the piston lrod engages a lever I9 which operates. the contact 20 `of an electric switch, this contact being so arranged that 'when the piston is in its middle position, lthe contact 'lies between vtwo cooperating contacts 2 I,"j22`, but when it is moved in one direction Aorthe other it engages one or the other'of these contacts. a reversing switch 23 at the contacts 124, 25 respectively thereof, andthe other contacts of this switch 25, 21 are connected to two indicatinglamps 28, 29 respectivelyand throug'hthem to a battery 40 from whichthe circuitis completed by a line 4I to the switch contact-member 20 aforesaid. Conveniently, the, lamps'A 28 and 29, are marked or coloured, say green'and red respectively, to make them more distinctive'.

An indicator is provided for the deviceto The twocontacts 2l, `22 are connected to The switch 23'is`cdup1e'd as indicated diagrammatically at 42 tothechange-over-valve I3 `so that adjustment of the change-over-valve from.,

one of its settings to the other reverses the circuit connections of the switch 23. i

In the operation of this device, assuming that the piston 4 is in its middle position as indicated, and that a tension load is Yapplied between the members 5 and I, the oil inthe chamber V I 0 is put under compression, and in the .particular settingv of the change-over-valve illustrated, the pipe I2 isconnected to the pump I1 so that the nonreturndelivery valve ofthe pump prevents any escape ofY oil andthe pressure generated in the it'has been found in practice that with adevice ofVv this typethere is a risk of the piston sticking in the cylinder, in which casevvserious errors areiri-V troduced. j Y In .order toL obviate all these errors, the apparatus isused in the following manner:

If the load has been applied to the piston 4 and it hasmoved towards Vtheright-hand end of the cylinder, thecontacts 20, '2| engage one another anda circuitis therefore provided lightingup the e green lamp 28. The hand-pump I'I is-then operated tofpump oil into thechamber I0 so as to move the piston backtoits datum or middle posi'- tion.V is indicated by Athe lamp 28 being no longer illuminated,A since the circuit is broken at thecontacts .23, 2| by the return movement of thepistonjto its middle position. The pressure indicated on the gauge I8 is thenA a true measure of the load and it is further ensured that the pistonis always in the same condition when making the measurement and that it ismoving freely in the cylinder atthetime whenthe measurement is made; any loading due to out-of-balance of the whole assembly Vwhen used in the torque-v Vmeasuring device above mentioned, is thereby reduced to aminimum.

InV describing the operation it wa'sa'ss'umed that the change-over-valve yI3 was set in the position indicated in` the drawingk and that the applied load tended to move the piston towardsthe right. If alternatively, the change-over-valve I3 had beenin its other position so that the chamber I0 was open to drain, the application of the tensile e load would not be opposed and the piston would be moved bythe load. In order to prevent too L sudden movement, the outlet from the drain pipe YIII to the reservoir I6' is preferably restricted as shown at ,43 'so as to allow only a slight discharge of the oil. With this setting of the change-overvalve I3, howe ver, the reversing switch 23 will Vfalso be in its other 'setting and the closure of the g Vcontacts 20, 2l would complete the circuit through the red lamp 29. The lighting -up `of this llamp immediately shows the operator that .the changeover-valve I3V should be reversed and when he makes Vthe necessary adjustment, the 'simultaneous. adjustment ofthe switch 23 would cause the green lamp 2B to be lighted. The use of these two lamps therefore simplifies thefoperationof yof the valve 2,403,194 j i Y is 4 i the device. As soon as the load is applied, if the red lamp lights up the operator knows that he must reverse the "change-over-valve I3 thereby lighting the green lamp. When the green lamp is'alight the operator works the'pump I1 until the green lamp is extinguished and then reads off the pressure on the gauge I8. If when the load is applied the *green lamp lights up, the operator knows that he need not reverse the setting I 3, but can proceed with the pumping lfortl'i'vvith.

The use of the restricted outlet 43 on the drainV pipe I4 also safeguards the apparatus against j sudden removal or reversal of the load. It is also desirable that the outlet I3Y from thev drain pipe should' communicate with the oil reservoir t6 at a point below the surface of the oil therein. This ensures that when the piston moves to increase the volume of the chamber whichr is connected to drain, oil will be sucked in so as to keep' the chamber full. Preferably, therefore, the reservoir IB is arrangedat the same level asor above, the cylinder to ensure that the cylinder is'maintained full of Oil. Y

In applying the invention tothe apparatus described iny prior United States Patent No. 2,362,308, granted November 7. 1944, very high pressure, of 2,000 to 3,000 lbs. per square inch or more may be developed, and it is therefore ldesirable that the sealing arrangements on ythe cylinder and piston should be as effective as possible. pared with its diameter for this purpose `.and provided with sealingV grooves on Vits periphery. It will be appreciated, however, that since the piston isb'roughtito its datum position by supplying oil to the cylinder before a measurement is taken, any leakage which may have occurred is compensated by the use of the pump.

Iheapparatus above described hasfthe advantagey over known forms of apparatus'for a similar purpose in that it is sensitive to' small changes of load, whilst being capable of registering very Y high loads, and it does nottend to stickjin any position or positions over its operating range.

. I claim:

,1. In apparatus for measuringftensile or compression loads, the combination with a hydraulic cylinder and piston to convert the load into hydraulic pressure, and a pressure measuring gauge. of a single pump arranged to deliver a liquid into that end of the cylinder towardswhich the piston has been moved by the applied load for forcibly returning theupiston to a neutral position before the pressure reading is taken, and a change-over-valve whereby the pump can supply either end of the cylinder and having a connection to drain. .y

2. Apparatus according to claim 1, wherein the der .from which theypiston has been moved byA the applied load. y Y e,

4. Apparatus accordingjto claim 1, wherein the change-over-valve connects alternatively either ,end of the .cylinder tothe pump and the other endto a reservoir from which the pump'is supplied. Y y' 5. Apparatus according to claim 1,-Whe1ein the connection to drain is restricted, Vfor the purpose set forth. Y, r

Y WILLIAM The piston may be made very longcom- Y 

